A display apparatus using a plasma display panel has been watched with keen interest in recent years, as a color display device capable of realizing a large size, a thin type and light weight, in a field of a color display device used for image display of a computer or a television set.
In a plasma display panel, a large number of discharge cells each being filled with discharge gas are provided between two glass base boards each being equipped with electrodes. The discharge cell is provided with a phosphor layer, and is arranged to generate vacuum ultraviolet rays when voltage is impressed between the electrodes for selective discharge, whereby the phosphor is excited to emit visible light.
As a phosphor instituting a phosphor layer, in this case, there is generally used a material wherein activators are dispersed in a base material shown below (Non-patent Document 1).
“Blue light emitting phosphor”: BaMgAl10O7 “Green light emitting phosphor”: Zn2SiO4:Mn “Red light emitting phosphor”: (Yx, Gd1-x) BO3:Eu
Incidentally, a color display device such as a plasma display panel has a problem that aging luminance deterioration is remarkable, namely, a problem that a life is short.
As a cause for the aging luminance deterioration, there are given vacuum ultraviolet rays which are generated by discharge in the plasma display panel in the case of driving it, or an ion impact, which damages a phosphor and causes its luminance deterioration. In the case of a green light emitting phosphor, in particular, its luminosity factor is higher than those of other colors, and therefore, drastic deterioration of white luminance and changes in chromaticity are undesirably caused on a plasma display panel, even when the phosphor is deteriorated slightly.
For preventing aging luminance deterioration, therefore, Patent Document 1 discloses a trial wherein a base material of a phosphor and an activator material are baked, then, base materials of phosphors are further mixed therewith to be baked, in which a period of time and temperature of the baking are controlled to regulate activator concentration (% by weight) so that the activator concentration (% by weight) inside a phosphor particle may be lower than that in a superficial portion of the particle, to prevent crystal deformation of the phosphor particle caused by an Mn dope representing an activator.
Further, in addition to the problems stated above, there has been a problem that electric charge characteristics are deteriorated in a color display device. A cause for the deterioration of the electric charge characteristics is low stability in the case of driving a plasma display panel for discharging. If stability in the course of discharging is low, there is caused a discharge failure such as discharge fluctuation or no occurrence of discharge, which remarkably deteriorates display quality.
For preventing the deterioration of the electric charge characteristics for the green light emitting phosphor containing Mn that serves as a major emission, therefore, Patent Document 2. discloses a trial wherein the deterioration of the electric charge characteristics is improved by enhancing stability in the course of discharging, by charging a phosphor from 0 to the positive electrode side, by the use of (1) a means to cover with oxides which positively charge a surface of a phosphor particle, for positive electrostatic charges, or (2) a means to smash a phosphor particle to make a fresh surface of the particle to be exposed, for positive electrostatic charges.
(Patent Document 1) TOKKAI No. 2004-91622
(Patent Document 2) TOKKAI No. 2003-18365
(Non-patent Document 1) “Electronics Jisso Gijutsu” p. 23-p. 26, 1977, Vol. 13, No. 7